At present，most of the materials in the electrical field are polymer composite materials. Conventional mechanical and physical detection methods often fail to meet the requirements for testing internal defects. From practical considerations，destructive experimental methods cannot be used for testing，so non-destructive testing methods must be carried out. There are many non-destructive testing techniques widely used in the internal structural defects of composite materials，including radiographic inspection，ultrasonic inspection，infrared thermal wave imaging inspection，optical holography technology，etc. The first three are the most widely used，but there are also many restrictions in the field of electricalmaterials.Anewmethodbasedonfrequency-modulatedcontinuousterahertzwaveisusedtodetectvariousdefects ofelectricalmaterials.Asaresult，somedefectshavebeensuccessfullytestednon-destructively.Consideringthattheenergy oftheterahertz waveislowandithasstrongpenetratingpower tonon-polarmaterials，thisdetectionmethodmakesupfor someshortcomingsofnon-destructivetestingtechnologysuch asfastdecay orhighenergy，whichhaspositivesignificance inthefield.